The invention pertains to the field of window framing for commercial, industrial and residential windows and, in particular, to extruded frames for single or multiple glazed windows.
For many years window frames constructed of extruded aluminum have been widely available for commercial and residential buildings. Such frames are weather resistant for extended periods of time. In particular, they are resistant to moisture, heat and solar ultraviolet degradation. The aluminum framing, however, is highly heat conductive and severly degraded and corroded by salt mist at seashore locations. To reduce the thermal conductivity of aluminum framing, modern framing incorporates vinyl plastic breaks between inside and outside portions of the frame. To reduce the salt mist corrosion, modern aluminum framing incorporates a hard anodized surface treatment or a salt and weather resistant surface coating such as plastic or paint.
With the exception of marine window frames such as that disclosed in U.S. Pat. No. 3,868,789, window frames constructed of extruded plastic have not become generally available in the market place. U.S. Pat. No. 4,110,942 illustrates a polyvinyl chloride extruded window frame mullion with appendages that may be selectively trimmed depending on the position of the frame member in the window.
Until recently most plastics suitable for extrusion as window frames have been severely degraded by ultraviolet radiation or otherwise structurally inadequate for window frames. Plastic materials that are resistant to ultraviolet degradation have been unsuitable for extrusion or otherwise unsuitable as the structural component of the window frame.
To overcome the above limitations various composite constructions have been proposed. U.S. Pat. No. 3,492,770 illustrates an aluminum frame covered by interlocking dovetailed plastic pieces. Such a construction, however, is unduly complicated. U.S. Pat. No. 3,918,231 illustrates a less complicated means for attaching a plastic cover piece to a metal window frame. U.S. Pat. No. 4,189,520 illustrates window or door structural framing of polyvinyl chloride coated with polymethylmethacrylate to improve the weatherability and ultraviolet resistance of the framing.